The development of techniques which allow the efficient introduction of foreign genetic material into the germ line of animals has made it possible to analyze controls of mammalian development by a combined molecular and genetic approach. In this research proposal previously established methods will be used to introduce genes or cells into the developing mouse embryo. The main goals of these experiments are (1) identification and characterization of genes which are crucial for early development; (2) understanding the function protooncogenes may have in mammalian embryogenesis and the effect of oncogene expression on the developing mouse embryo; (3) The study of patterns of migration and homing of normal and transformed cells in the developing mouse embryo. 1) Insertional mutations will be induced by inserting retroviruses into the germ line of mice by an experimental approach which was successful previously in derivating a lethal mutation of the a1(1) collagen gene. Furthermore, procedures will be established for genetically rescuing mice carrying lethal mutations. As a first approach we will attempt to rescue the collagen mutation on the germ line level by microinjection of the wild type gene into mouse zygotes and on the somatic level by microinjection of a vector transducing the gene into mutant embryos prior to their developmental arrest. 2) Protooncogenes, oncogenes or temperature sensitive mutants of oncogenes will be introduced into the developing mouse embryo by retrovirus infection or by microinjection in the zygote. The expression of the inserted genes will be controlled by tissue specific or inducible promoters. These experiments are designed to test the normal function of protooncogenes in mammalian development and to determine the oncogenic potential of oncogenes. 3) Previous experiments have shown that neural crest cells can be introduced into midgestation embryos and participate in normal morphogenesis. We will use this approach of introducing cells into the developing embryo in an effort to define the parameters that determine the migration and homing of normal and transformed cells in n embryonic environment.